Although Cohen continued to write TV and film scripts during the 1970s – such as Columbo – he further turned his hand to directing. His directorial debut was the comedy film Bone starring Yaphet Kotto, aka Beverly Hills Nightmare, Dial Rat for Terror and Housewife. In 1974 he directed the horror filmIt's Alive, about a mutant monster baby that embarks on a killing spree. The film – an initial commercial failure – was re-released with a new and sharper advertisement campaign; it went on to earn over $7 million for Warner Bros. and spawn two sequels.[5] Cohen followed-up It's Alive with the science fiction-serial killer film God Told Me To (1976), in which a New York detective investigates a spate of killings by apparently random people who say that God told them to commit the crimes. He would concentrate his work predominantly within the horror genre throughout the 1970s and 1980s, often incorporating elements of crime, police procedural, and science fiction with scathing social commentary.[2]

Cohen created the It's Alive series in 1974 when he made the film It's Alive. The film was eventually a moderate success – after a re-vamped advertising campaign[5] – and went on to spawn two sequels, It's Alive II: It Lives Again (1978) and It's Alive III: Island of the Alive (1987).[16][17][18]

It's Alive (1974) tells of a young couple, Frank and Lenore Davis, who give birth to a mutated baby. The doctors and nurses at the hospital attempt to end the life of the deformed child but it instead kills them and escapes. A police manhunt ensues as the fleeing mutation leaves dead bodies in its wake. Frank sees the child just as Dr. Frankenstein saw his monster and assists the police. The emphasis in It's Alive is on chemicals in the ecosystem and experimental prescription drugs that can be harmful to unborn babies. The score for It's Alive was composed by Bernard Herrmann, famous for his contributions to many Alfred Hitchcock films, including Psycho, North by Northwest, and Vertigo. In fact, the welling strings, horn arrangements and harp glissandos throughout the film portend the soundtrack to Herrmann's final film score two years later for "Taxi Driver". The cast includes John P. Ryan, Sharon Farrell, James Dixon, and Andrew Duggan.[19]

It Lives Again (1978) picks up where the first one ended. More mutated babies are appearing around the country. Frank has now joined a renegade mob who are attempting to stop the government from killing these strange mutations. The emphasis in It Lives Again is on accepting one's child, even if it is born with deformities or disabilities. The score is again provided by Bernard Herrmann. The cast includes John P. Ryan, James Dixon, Andrew Duggan, and Frederic Forrest.[20]

Joseph Rusnak remade Cohen's It's Alive in 2008.[21] Still awaiting a score on Rotten Tomatoes, the existing reviews are also very poor.[22] Even Cohen admitted that the remake was dreadful[23] and states: 'It’s a terrible picture. It’s just beyond awful'.[24] Cohen offered his 1974 script but remarks that it was completely ignored: "I would advise anybody who likes my film to cross the street and avoid seeing the new enchilada."[24]

Critical response to Cohen's work has been extremely varied, reviews ranging from good to poor.

Cohen's science fictionhorror film and satirical social commentary The Stuff (1985) garnered mixed reviews, often being compared to Jack Finney's The Body Snatchers novel and the 1958 film The Blob. It has a moderate fresh rating of 63% on Rotten Tomatoes.[29] The Apollo Movie Guide remark that The Stuff works on a purely visceral level and that it further achieves a tongue-in-cheek social parody of a society that cannot help buying into the latest craze. Although Apollo praise the juxtaposition of Cohen's clever screenplay and Michael Moriarty's performance, it states that the film is no classic. It does, however, award the film a modest Apollo Rating of 77/100.[30] The Chicago Sun-Times, on the other hand, sees The Stuff as a widely ambitious movie that fails mainly due to distracting glitches and a lack of plausibility: "What we have here are a lot of nice touches in search of a movie." Chicago Sun-Times rating: 1 1/2 stars out of 5.[31]Bloody Disgusting nevertheless awarded The Stuff 3 stars out of 5, pointing out both the good and the bad: "[I]t's smart, it's relevant and it has some bad acting. [It should be] enjoyed for all the wrong and some of the right reasons that it is not just a horror movie, but a very honest and important movie as well."[32]

His fantasyhorrorQ aka Q: The Winged Serpent' (1982) has a Rotten Tomatoes rating of 61%.[33]TV Guide praise Cohen for his intelligence, creativity and originality and further comment that '[Cohen] successfully combines a film noir crime story with a good old-fashioned giant monster movie' and that 'Michael Moriarty turns in a brilliant performance as Jimmy Quinn [...]'.[34] Horror author and movie critic, Kim Newman, praises Cohen's plot originality and canny use of characters in Empire, pointing out the director's use of an oddball as lead – Jimmy Quinn – who would ordinarily be a secondary character or warrant solely a cameo appearance; Newman also explains how Cohen has relegated all the usual plot devices – in movies such as King Kong – to the background.[35] Alternatively, the Chicago Reader, although viewing Cohen's monster movie as 'cheesy' and 'fun', ultimately condemns the movie as being 'curiously disengaged and sloppy'.[36]The New York Times, following the film's opening day at the Rivoli Theater, had just 'a few words – only a very few – about Q, offering a brief neutral synopsis and a couple of quotes.[37]Variety are more favourable, focusing on Cohen's 'wild' and 'bizarre' – albeit realistic – efforts: Q has great fun mixing realistic settings with political satire and a wild yarn'. They go on to say that the film belongs to both Moriarty and the Monster.[38]

It's Alive, the first part of Cohen's horror trilogy featuring a mutated baby that kills its prey when trapped or frightened, holds a rating of 67% on Rotten Tomatoes, one of the highest rated Cohen films from the latter. Focusing on the social context of the film at the time, The Film Journal points out that It's Alive 'carries a potent mix of both suspense and social critique [...] [i]nvoking such taboo subjects as abortion as early as 1974'. As well as being apt at providing 'suspense', The Film Journal acknowledge Cohen's ability 'to impart an intelligent nature to his otherwise pulpy horror films'.[39]Black Hole magazine say that despite a lack of A-List actors and special effects, It's Alive still manages to maintain the viewers interest due to Cohen's 'unique horror concept and a script rich in ideas'. Black Hole nevertheless points out that '[w]hile the drama is consistent, it's less successful as a seventies monster movie, and especially lacking now': whereas Jaws (1975) revealed the shark slowly, Cohen's film 'barely ever shows us the goods'. The magazine does agree, however, that It's Alive was 'a sufficiently powerful monster movie and [that] audiences wanted more'.[40]Filmcritic draws attention to the humour element, especially the scenes where the Baby-Monster is rustling in the bushes, unseen, comparing them to the scene in Basket Case (1982) when the Baby-Monster is stuffed into a garbage sack after being cut away from its human twin. Basket Case is indeed a part of another – later – Baby-Monster horror trilogy. In short, Filmcritic says that Cohen's film should not be confused with art; and yet, it is 'pretty scary stuff' that 'manages a few neat tricks'.[41]

God Told Me To aka Demon (1976), Cohen's science fictionthriller, has a rating of 75% on Rotten Tomatoes, making it Cohen's most successful directorial effort, critically. The film, in which a number of New York citizens embark on a killing spree because God Told Them To, is called 'one of his most ambitious movies' that is 'cemented in an interesting idea' by QNetwork Entertainment, who find Cohen's ideology of the existence of God interesting: 'cynical at best' and 'sacrilegious at worst'. The magazine continues, however, to comment on Cohen's lack of patience and drive when completing his movies, regarding the end products as being 'hastily thrown-together' and 'a mosaic of scenes, rather than a satisfying whole'. In conclusion QNetwork give the film an even 2 1/2 stars for being the 'clumsiest and most entertaining schlock of the last 20 years'.[42]CinePassion online magazine simply state: '[a] work of genius, in other words, possibly the Cohen joint that brims with the most all-pervasive invention and danger, as radical a Seventies 'incoherent text' as Taxi Driver and a clear linchpin of The X-Files'.[43] The Chicago Sun-Times sees Cohen's incoherent text in a different light, likening the film to a cinematic version of the card game 52 Pickup: 'the movie does achieve greatness in another way: this is the most confused feature-length film [...] ever seen'.[44] But Time Out applaud Cohen for offering 'the perfect existential anti-hero' in New York cop, Lo Bianco, in a film that 'overflows with such perverse and subversive notions that no amount of shoddy editing and substandard camerawork can conceal [its] unusual qualities' and that by '[d]igging deep into the psyche of American manhood, it lays bare the guilt-ridden oppressions of a soulless society'.[45]